JPH01218124A - Driving circuit for semiconductor switch - Google Patents

Abstract

PURPOSE:To prevent the delay in turn-off through the application of reverse bias to transistor(TR) at reset operation of a current transformer and to prevent the increase in the turn-on loss of a semiconductor switch by connecting a diode of a reset circuit in parallel between the base and emitter of the TR of a power Zener diode. CONSTITUTION:A 1st TR 1, a 1st diode 6, and a 1st Zener diode 11 are provided to the circuit. In order to ensure the reverse bias of a 2nd TR 15, the diode 12 of the reset circuit consists of the series connection of two diodes 12a, 12b. A 2nd Zener diode 13 and a 2nd TR 13 constituting the power Zener diode circuit are provided. A 3rd diode 16 inserted blocks the forward current of the current transformer 3 when the semiconductor switches 1, 2 are turned on. Thus, even when the power Zener diode circuit is in use, the delay in the turn-off of the TR is prevented to reduce the turn-on loss of the semiconductor switch.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor switch formed by connecting a bipolar transistor and a MOSFET in series, and particularly to a drive circuit for a current transformer feedback system.

[Conventional technology]

Figure 3 shows, for example, INTERNATIONAL RECT
IFIER's 'HEXFET DATABOOK'
This is a basic circuit diagram of this type of semiconductor switch shown on page 3 of A-1 Engineering (published in 1982).

In the figure, a bipolar transistor (hereinafter simply referred to as a transistor) (1) and a MOSFET (21) refer to the emitter E of the transistor (1) and the MOSFET (21).
is connected to the drain D to form a semiconductor switch. In (3), its primary winding (3a) is a transistor (1)
is a current transformer connected between the collector of 1) and the source S of MOS FET (21 is connected to terminal N. (4) and (5) are transistors (1)
A capacitor and a Zener diode, (7) respectively connected between the base B and the terminal N of the transistor (1) (81 are a diode and a resistor, respectively, connected between the collector C and the base B of the transistor (1), (9) αα is terminal P
A DC power supply and a load are respectively connected between N and N.

Next, the operation will be explained with reference to FIG. 4 as well. First, before time t1, the gate voltage V of MOSFET (2)
GS is zero, transistor (1) and MOSFE
T(2) is in the off state and the primary winding of current transformer (3) (
3a), the capacitor (4) is charged through the diode (7) and the resistor (8), and the voltage VC across it is clamped to about 15V by the Zener diode (5).Next, at time t1, the MOSFET (2) Raising the gate voltage VGS from zero to a positive value MOSFET
When (2) is turned on, a discharge current, that is, a base current 113 flows from the capacitor (4) to the transistor (1) and MOSFET (2), so that the transistor (1) is also turned on immediately. As a result, the DC power supply (
9), the collector current IC of the transistor (1) starts flowing through the load αQ. At this time, if the turns ratio of the current transformer (3) is n, the secondary winding (3b) has ■cT2=
■A current of C/n flows, and this current flows through the diode (6),
Flows through transistor (1) and MOSFET (2). Thus, the positive feedback effect of the current transformer (3) supplies the base current IB to the transistor (1) to maintain the on state of the transistor Q).

Next, at time t2, the gate voltage V of MOSFET (2)
When GS returns from positive to zero, MOSFET (2+) turns off immediately. As a result, the emitter circuit of transistor (1) becomes essentially open, so that the collector current I
C goes from collector C to base B and becomes a capacitor (4)
and flows to the Zener diode (5).

At this time, the capacitor (4) acts as a means for suppressing the switching surge voltage between the drain D and source S of the MOSFET (21), and the blocking ability between the collector C and base 3 of the transistor (1) is restored.

At time t3, the collector current IC is cut off, and the transistor (1), MOS FET (21) and current transformer (3
The voltage VPN across the series body of ) rises to the level of the DC power supply voltage VE and is turned off.

By the way, at time [3, the collector current IC is cut off (3b
), an overvoltage of the reset voltage vreset is applied in the opposite direction as shown in FIG. Furthermore, Zener diodes (5) for small currents are generally easily available, but those for large currents are difficult to obtain. FIG. 5 shows a partial modification of the circuit shown in FIG. 3 in order to solve the above problem.

That is, in Fig. 5, after time [3], current transformer (3) 2
In order to suppress overvoltage generated in the secondary winding (3b), a reset circuit consisting of a Zener diode circle and a diode @ is inserted between both terminals of the secondary winding (3b). Furthermore,
In place of the Zener diode (5) in Figure 3, a Zener diode aJ, a resistor (14) and a transistor 0
A power Zener diode circuit is constructed to increase the current withstand capacity of this part.

[Problem to be solved by the invention]

The power Zener diode circuit in the conventional semiconductor switch drive circuit is configured as described above.
Although the current withstand t is large, on the other hand, the turn-off of the transistor a8 is delayed, which may cause problems.

That is, when the turn-off of the transistor α9 is delayed after time [3], the charge stored in the capacitor (4) is discharged and the charging voltage decreases (as shown by the dotted line in Figure 4 VC). There is a problem in that the base current IB at turn-on is insufficient, the turn-on time becomes longer, and the turn-on loss of the semiconductor switch increases.

An object of the present invention is to prevent a delay in turn-off of a transistor even when a power Zener diode circuit is used, and to reduce turn-on loss of a semiconductor switch.

[Means to solve the problem]

In the power Zener diode circuit of the present invention, the diode of the reset circuit is connected in parallel between the base and emitter of the transistor of the power Zener diode circuit.

[For production]

In this invention, during the reset operation of the current transformer, the second
The voltage generated in the diode of the reset circuit on the next winding side applies a reverse bias to the transistor of the power Zener diode circuit, which accelerates the turn-off of the transistor.

〔Example〕

Hereinafter, an example #J of this invention will be explained with reference to the drawings. In FIG. 1, (1) to 0 are the same as in the prior art, so their explanation will be omitted. However, in order to distinguish each circuit element, (1) is called a first transistor, (6) is called a first diode, and OD is called a first Zener diode. In addition, as described later, the diode uz of the reset circuit is connected to the second diode (xza) and the second diode (x
zb) in series. The a3α group also constitutes a second Zener diode and a second transistor, respectively, constituting a power Zener diode circuit, as in the conventional case.

The decoy is a newly inserted third diode that blocks the forward current of the current transformer (3) when the semiconductor switches +11 to +21 are on.

Next, the operation will be explained with reference to FIG. 2, but the on/off operations (times 1 to 2) of the semiconductor switches +11 to [21] are the same as in the prior art, so the explanation will be omitted. After the time t3 when the blocking ability between the collector C and the base 8 of the first transistor (1) is restored, the secondary winding (3b) of the current transformer (3)
A reset voltage yreset is generated in , which causes a current to flow through the reset circuit, and the second diode (
lza) (1zb) is applied to the second transistor (15
1 will be applied with a reverse bias. As a result, the turn-off operation of the transistor α9 of the cylinder 2 becomes faster, and the discharge of the capacitor (4) is prevented. Therefore, it is possible to prevent the turn-on loss from increasing due to a delay in the turn-on time of the semiconductor switch.

〔Effect of the invention〕

As described above, in the power Zener diode circuit of the present invention, the diode of the reset circuit is connected in parallel between the base and emitter of the transistor of the power Zener diode circuit. A reverse bias is applied to the transistor to prevent a delay in its turn-off, thereby preventing an increase in turn-on loss of the semiconductor switch.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a semiconductor switch drive circuit according to an embodiment of the present invention, FIG. 2 is a time chart explaining the operation of the circuit in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional basic drive circuit. FIG. 4 is a time chart explaining the operation of the circuit shown in FIG. 3, and FIG. 5 is a circuit diagram showing another conventional drive circuit. In the figure, (1) is the first transistor, (2) is M
OSFET, (31 (3a) and (3b) are respectively current transformers, their one missing winding and their secondary windings, (4) are capacitors, (6) are the first diode, (5) are the first Zener diode, (xza) (1zb) is the second diode, (131 is the second Zener diode, 051 is the second transistor, αe is the third diode. Note that the same symbols in each figure are the same or A considerable portion is shown.

Claims (1)

[Claims] A semiconductor switch is configured by connecting a first transistor and a MOSFET in series to the main current path by connecting their respective emitters and drains, and a secondary winding in which a primary winding is connected in series with the semiconductor switch. One end of the wire is connected to the base of the first transistor through a first diode, and the other end of the secondary winding is connected to the source of the MOSFET, respectively, to supply a base current to the first transistor. a capacitor connected between the base of the first transistor and the source of the MOSFET; a charging circuit for the capacitor connected between the collector and the base of the first transistor; A reset comprising a first Zener diode having an anode connected to one end of a secondary winding, and a second diode having a cathode connected to the cathode of the first Zener diode and an anode connected to the source of the MOSFET, respectively. The circuit includes a second transistor having a collector connected to the base of the first transistor, an emitter connected to the source of the MOSFET, an anode connected to the base of the second transistor, and a cathode connected to the first Zener diode and the second transistor. a third diode connected to the connection point with the diode; and a second Zener diode, the anode of which is connected to the base of the second transistor, and the cathode of which is connected to the collector of the second transistor. Semiconductor switch drive circuit with Zener diode circuit.